The present invention relates to a recording circuit in a magnetic recording and reproducing apparatus and more particularly to a magnetic recording circuit suitable for use as a recording circuit for video signals in a video tape recorder (VTR) of, for example, a helical scan type, a recording circuit of a voice FM recording and reproducing apparatus or a bias current circuit for controlling a bias current supplied to a recording head of a tape recorder.
A magnetic recording and reproducing apparatus such as a VTR or a tape recorder has in its recording circuit for voice signals a bias current circuit. To record a voice signal, the voice signal is superimposed on a bias current in order that upon reproduction of the voice signal, waveform distortions can be suppressed. However, where the bias current supplied to a magnetic head does not have a proper value, the reproduced voice signal will be degraded in its frequency characteristics, decreased in its level and accompanied by an increased waveform distortion. To cope with this problem, it is a practice to provide in the bias current circuit a variable resistor for adjustment of the level of the bias current. In mass production of magnetic recording and reproducing apparatus, level adjustment for the variable resistors is very time-consuming and troublesome. In addition, for ease of the adjustment, layout of the variable resistors must be taken into consideration and the degree of freedom of design is impaired.